The role of vitamin A as an immune modulatory factor has been the focus of many studies both in animals and man. Epidemiologic studies emphasize that vitamin A is essential for supporting the immune system against infection. Despite many therapeutic improvements in recent years, infection still remains a major problem in very low birth weight (VLBW) pre-term infants. Pre-term infants have lower plasma vitamin A (retinol) levels and limited hepatic reserves compared to full term infants. Vitamin A deficiency may lead to increased susceptibility to infection in pre-term infants. Hepatitis B immunization in the neonatal period offers an excellent opportunity to determine what effects vitamin A supplementation has in pre-term infants on their antibody immune response to this vaccine. VLBW pre-term infants less than 1500g (less than 32 weeks gestation) will be randomized into two treatment groups: vitamin A supplemented and placebo (saline). The vitamin A treatment group will receive 2000 IU of retinyl palmitate by intramuscular injection starting on postnatal day 2 and thereafter on alternate days for 28 days. Plasma vitamin A levels will be closely monitored for toxicity. Plasma immunoglobulins and antibodies to HbsAg and tetanus toxoid will be quantified by ELISA after the second and third doses of hepatitis B vaccine. These results will be correlated with changes in CD4+ T-cell subsets as defined by their cytokine secretion profile and the proportion of naive (CD45RA) to memory (CD45R0) T-cells as analyzed by flow cytometry. Acceleration in the maturation of T-cells (naive to memory), and augmentation in the proportion of intracellular cytokine producing T-cells will provide a mechanism for the enhancement in the humoral immune responses to hepatitis B vaccine by vitamin A supplementation. Finally, the type and number of infections in the NICU and to 9 months of age will be recorded to determine if vitamin A supplementation affects the incidence and severity of infection in early infancy. Vitamin A supplementation may be useful in pre-term infants in augmenting B-cell immune responses to infectious agents and in their response to vaccines. These factors could lead to decreased morbidity and mortality of pre-term infants during early postnatal life.